I'm running first scenario of WFRP3 next monday and it just happens to be Solstice (and the stars are naturally right). I've a haunted village with roads leading nowhere so I'm thinking there must be Changer of the Ways loose. But what Old One could be used as an aspect of Tzeentch? Or as I like to put it whose avatar Tzeentch is?

I'm thinking Black Goat of the Woods (as it would be quite suitable for WFRP and I'm NOT going to use Nyarlothotep. His masks are EVERYWHERE! )

Nyarly actually seems the closest, since he likes to mess with humanity and walks among us. The King in Yellow maybe?

Agreed- Nyarlathothep and Tzeentch are pretty much the same in concept. In fact, given that both are malicious tricksters with near-infinite guises and a fondness for Sorcery among their followers they could very easily be the same deity in different guises...

The King in Yellow as mentioned above (Hastur) and The Haunter of the Dark (Nyarlathothep) are both good examples of Lovecraftian deities manifested in a more limited form on this plane. They are easier for mortals to comprehend and, more importantly in an RPG setting, sufficiently weaker in these guises that a PC group has a chance of beating them.

For those who have The Enemy Within campaign, the alternate "Apocalyptic PCs Fail" ending to Shadows over Bogenhafen has a very good description of Tzeentch manifesting.

Maybe The Colour of The Space? If i recall properly it was Yogsothoth. In story he also made happening some weir sh**. He could fit in to Warhammer pretty well with his many colours and ability of bending reality. But i don't remember story to well so I may be wrong.

I think that it was a star vampire but as wikipedia tells it was never revealed. In "At the Mountains of Madness" there's link between Yog-Sothoth and "colours out of space" so you might as well be right. As with other greater beings of Cthulhu Mythos Yog-Sothoth would suit Warhammer perfectly.